Insertion of tyrosinase minigene resulted in a small deletion (<200 kb) upstream of Sox9 on the mouse chromosome 11. This mutation (Ods) is associated with biallelic expression of Sox9 and development of testes in the XX fetal gonad. The proposed study is to test the hypothesis that Ods mutation harbors a long-range gonad-specific regulatory element that normally mediates the repression of Sox9 expression in the XX fetal gonad. It was predicted that Sox9 is the primary inducer of Sertoli cell differentiation, the key event in testis development, and possibly, a direct downstream target of Sry, the primary testis-determining gene on the Y chromosome. The first specific aim is to recreate Ods deletions in XY ES cells and generate new lines of mutant mice. This approach will prove that the mutation phenotype is caused by deletion and enable to shorten the deletion, so that the repressor binding elements can be more precisely localized. Once the deletion is minimized, its homologous region in the human will be identified and tested if mutations in this region are associated with sporadic and familial cases of XX(Y-) males. The second specific aim is to determine the number and chromosomal location of autosomal and/or X-linked genes involved in Ods sex reversal. The involvement of autosomal/X-linked genes has been suggested by the observation that Ods sex reversal is fully penetrant in the FVB background while only 10 percent penetrant in the A/J background. The dominant A/J allele will be identified by expression of the mutant phenotype in the F2 offspring from the cross of AFVF1 Ods/+ mice. The role of known candidate sex determining genes such as Dax1 and Sox3 will be, in addition, assessed in this system. The third specific aim is to examine the role of Y chromosome gene expression in spermatogenesis, taking the advantage of Ods sex-reversal. Male mice lacking Sry but containing all other Y chromosome genes (= XY Ods/+) will be produced and their fertility and spermatogenesis will be examined. To test whether expression of Y chromosome genes in somatic cells of the testis is necessary for spermatogenesis, normal spermatogonial stem cells carrying the lacZ reporter gene will be transplanted into adult XX Ods/+ testes. The XY non-transgenic male will be injected with busulfan, which blocks spermatogenesis, and serve as a control recipient.